Escaping the fire trap: Does frequent, landscape-scale burning inhibit tree recruitment in a temperate broadleaf ecosystem?

Frequent prescribed burning is commonly used to restore and maintain open forest ecosystems in temperate broadleaf regions of the eastern United States. Repeated surface fires reduce the abundance of small woody stems through top-kill or mortality, with implications for age structure and ecosystem development. In this study, we quantified tree recruitment patterns over two decades across two landscape-scale studies in Missouri: the Missouri Ozark Forest Ecosystem Project (a control, with no burning) and the Chilton Creek Management Area (burned on 2–3 year fire return interval). Through time, frequent burning reduced the rate of ingrowth (i.e., new trees entering the overstory size class, defined as ≥11.4 cm diameter at breast height (DBH)), and the effect of burning on the ingrowth rate was consistent across site types (summits, exposed backslopes, protected backslopes, or upland waterways). Two decades of frequent burning reduced the abundance of scarlet oak (Quercus coccinea) in the ingrowth population. In the unburned control, the proportional abundance of mesic species such as red maple (Acer rubrum) and blackgum (Nyssa sylvatica) increased during the study period; frequent fire controlled the population of red maple but resulted in a similar increase in blackgum abundance in the ingrowth population of the burned area. Our results indicate that frequent burning affects the tree recruitment process in multiple ways: 1) reducing the source population for recruitment by reducing midstory abundance; 2) increasing probability of mortality or top-kill during the recruitment period. Fire-free periods may be necessary to allow eventual replacement of canopy trees in temperate broadleaf open forest ecosystems.